At present, the wireless communication standardization organization is making discussions on the basis of a latency shortening technology for a Long Term Evolution (LTE) system in a handover process. In an existing LTE system, difficulties leading to handover latencies mainly lie in reconfiguration of a terminal, a source base station and a target base station.
In a conventional art, handover latencies include a downlink synchronization latency, uplink synchronization latency and reconfiguration completion signaling latency on a target base station side after reconfiguration of a terminal is completed. Here, since downlink synchronization focuses on synchronization between the terminal and a target base station, when the target base station is synchronized with a source base station, this step may be ignored. A reconfiguration completion latency is the same as a reconfiguration signaling configuration latency, and the key is a processing latency of the terminal. Therefore, the most important latency is the uplink synchronization latency.
At present, uplink synchronization mainly involves the following steps.
(1) A terminal initiates a contention-free random access flow according to preamble information configured in reconfiguration signaling.
(2) A base station calculates a Timing Advance (TA) of uplink synchronization after receiving the preamble information.
(3) The Base station notifies the TA to the terminal through a Random Access Response (RAR), and allocates an Uplink (UL) grant resource to the terminal.
(4) The terminal uses the configured TA at the UL grant resource to send a reconfiguration completion message.
In the conventional art, a specific optimization solution for the flow includes that:
a soft handover manner is adopted, that is, a behavior of the terminal in an existing LTE system is changed. During reconfiguration of the terminal, entities of Media Access Control (MAC), Radio Link Control (RLC), Packet Data Convergence Protocol (PDCP) and the like are not reset, that is, the terminal still reserves a Radio Resource Control (RRC) connection with a source base station; and meanwhile, the terminal performs downlink synchronization and uplink synchronization at a target base station, sends reconfiguration signaling, and only after the terminal is successfully connected to the target base station, cuts off the RRC connection with the source base station.
In the solution, the TA is obtained by adopting a solution of advanced measurement and calculation by the terminal, that is, after the terminal completes measurement reporting, the base station selects the target base station, and then configures a corresponding resource to the terminal to enable the terminal to perform uplink synchronization resource sending with the target base station, and after receiving such signaling, the target base station calculates the TA, and sends it to a source cell; and the source cell sends a handover command including the TA to the terminal after receiving the TA.
According to the solution, a latency caused by establishment of RRC connections in a handover process may be eliminated, but the terminal is required to support keeping of the RRC connections with both the source base station and the target base station, so that there are made high requirements on functions of the terminal, and complexity of the terminal is increased; and moreover, in the handover process, data transmission between the base station and the terminal is interrupted, so that data transmission efficiency of the system is low, and user experience is poor.